A polymeric actuator formed from a polymeric material, as compared with an actuator formed from materials such as a ceramic, a metal and the like, has features that it is lightweight and it has excellent flexibility. From these features, the polymeric actuator is collecting a lot of attention as an actuator, which is applicable to a sensor, an optical switch, a diaphragm, a Braille display, power generation applications such as wave power and heel power, industrial and nursing care robots, medical instruments and the like, and can safely operate if directly contacting with human skin. Various polymeric actuators, which are formed from an ion-exchange membrane, a conductive polymer, a dielectric elastomer, a polymer gel, a hydrogel, a carbon nanotube and the like, have been ever proposed.
However, since the actuator formed from the ion exchange membrane, the conductive polymer or the hydrogel is driven by movement of water or ions, it was difficult to drive the actuator in air. Therefore, a polymeric actuator formed from a dielectric elastomer, which it is unnecessary to use a solvent, was proposed. However, since a drive voltage for a deformation is high, which is several thousand V, in the polymeric actuator using the dielectric elastomer, it is required to further reduce the drive voltage for practical use.
Therefore, a polymeric actuator obtained by using a polyol, which is dielectric or has a substituent having relatively strong dipole moments, as a new polymeric material, for which the polymeric actuator can be driven in air, in elastomers such as a polyurethane elastomer or by adding a high dielectric constant solvent thereto has been proposed (Patent Documents 1 to 3).
Patent Document 1 discloses a polyurethane elastomer actuator, in which the polyol is oriented in the direction of an electric field by applying a DC electric field to a polyurethane elastomer which comprises a dielectric polyol or a polyol containing a substituent having relatively strong dipole moments. However, the polyurethane elastomer actuator has an improved flexibility and can drive in a low electric field by optimizing a molecular weight and the like of materials used, but a temperature dependability of physical properties is not described, and there is a problem that the dielectric breakdown strength is low because of high dielectric constant of the polyol.
Patent Document 2 discloses a high-speed response polyurethane gel actuator, in which dielectric molecules or substituents are oriented in the direction of an electric field and a structure of the gel is anisotropically changed by applying a DC electric field to a polyurethane gel-like material, which is formed by involving a dielectric solvent in a dielectric polyurethane elastomer or a polyurethane elastomer containing a substituent having relatively strong dipole moments. The polyurethane gel actuator has an improved flexibility and can drive in a low electric field by using a high dielectric constant solvent, but there is a problem that the dielectric breakdown strength is low because of using the solvent, which is a low molecular weight component.
Patent Document 3 discloses a dielectric film suitable for a transducer such as an actuator, a sensor and the like, which is formed by crosslinking an elastomer composition comprising an elastomer containing a heteroatom in a molecule and a high dielectric constant liquid compound containing a heteroatom in a molecule, which is compatible with the elastomer. The dielectric film has an improved flexibility and can drive in a low electric field by using a high dielectric constant solvent, but there is a problem that the dielectric breakdown strength is low because of using the solvent, which is a low molecular weight component.
Therefore, a polymeric actuator obtained by using a dielectric elastomer which has low temperature dependability of physical properties such as an elastic modulus and high dielectric breakdown strength, and which can drive in a low electric field is required.